A conventional bidirectional DC-DC converter includes: a first switch interposed between one end of a primary winding of a transformer and a first voltage positive terminal; a second switch interposed between the one end of the primary winding and a first voltage negative terminal; a third switch interposed between the other end of the primary winding and the first voltage positive terminal; a fourth switch interposed between the other end of the primary winding and the first voltage negative terminal; a coil; a fifth switch interposed between one end of the coil and a second voltage positive terminal; a sixth switch interposed between the one end of the coil and a second voltage negative terminal; a seventh switch interposed between one end of a secondary winding and the other end of the coil; an eighth switch interposed between the one end of the secondary winding and the second voltage negative terminal; a ninth switch interposed between the other end of the secondary winding and the other end of the coil; and a tenth switch interposed between the other end of the secondary winding and the second voltage negative terminal (see, for example, Patent Document 1).
Another example of conventional bidirectional DC-DC converter includes a transformer connecting a voltage-type full-bridge circuit connected to a first power supply and a current-type switching circuit connected to a second power supply. A snubber capacitor is connected to each switching element in the voltage-type full-bridge circuit, and a primary winding of the transformer, a resonance reactor, and a resonance capacitor are connected in series. A voltage clamp circuit composed of a switching element and a clamp capacitor is connected to the current-type switching circuit (see, for example, Patent Document 2).